G proteins, receptors and cellular calcium Flashcards
what is signal transduction
the bit in-between the ligand binding and the receptors response
3 types of cell surface receptor
G protein, ligand gated ion channels and receptors with intrinsic enzyme activity
structure of G protein
7 transmembrane domains. Ligand may bind at N terminus or between 7 domains depending on its size. May be too large to fit between 7 domains. C terminus is on intrinsic side
what happens when a ligand binds to a G protein
results in conformational change and is activated. The G protein then interacts with the GPCR activating the G protein by causing GTP to exchange for GDP. This causes the alpha and btea-gamme subunits to split.
how is the G protein turned off once it has interacted with the effecter
GTPase catalanes GTP back to GDP and the alpha and gamma-beta subunits join back together and the G protein is now inactive
How GPCR’s are classified
effectors usually interact with alpha subunit so they are differentiated upon alpha subunits a1 adreno -alpha q a2 adreno - alpha I b1 adreno - alpha s b2 adreno - alpha s m1 muscarinic - alpha q m2 muscarinic - alpha I m3 muscarinic - alpha q
what do the different alpha subunits activate
alpha q = phospholipase C
alpha I and s = adenyl cyclase
how does the cholera toxin affect GPCR’s transducing signal
it prevents GTPase activity regulating in a continuous signal which is very dangerous and can lead to death
how does the pertussis toxin affect GPCR’s effect
it prevents signal from reaching the effector (whooping cough)
how does adenyl cyclase activation occur
Gs coupled receptors will activate this pathway. alpha will activate adenyl cyclase which catalyses ATP to cMAP. cAMP acts as second messenger and activates PKA
how does adenyl cyclase inhibition occur
Gi coupled receptors will prevent activation of adenyl cyclase so ATP isn’t catalysed to cAMP.
structure of PKA and how it works
2 regulatory units to which cAMP can bind and 2 catalytic units which are released when cAMP binds and phosphorylate specific proteins
phospholipase C activation
q coupled receptors activate phospholipase C which hydrolyses PIP2 to form IP3 and DAG. IP3 acts as second messenger and binds to calcium channels on the ER increasing levels of calcium in the cell. Some calcium then binds to PKC which is bound to DAG
how does signal amplification occur
uses of enzymes allow signal amplification every time an enzyme catalyses substrate and it produces multiple products
explain how vasoconstriction occurs
noradrenaline interacts with a1 adrenoreceptors using phopholipase and alpha q coupled receptors. this results in the release of calcium and phosphorylation of proteins needed for contraction
